Liquid crystalline oriented films are required to have good transparency and superior electrical and mechanical properties. Polyimide films satisfying these requirements find extensive use as the liquid crystalline oriented films. The polyimide films have excellent electrical and mechanical properties and also have a good transparency, but the transparency is a colored transparency. Therefore, it has been demanded to develop polyimides free from such coloration.
To this effect, various polyimides have hitherto been proposed. Of such polyimides, the aromatic polyimide having a recurring unit shown below has a small degree of coloration and high transparency and is useful as an excellent polyimide oriented film, as disclosed in Japanese Patent Application (OPI) No. 91430/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be the same or different, each represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a chlorine atom, or a bromine atom; R.sub.5 and R.sub.6, which may be the same or different, each represents a hydrogen atom, a methyl group, an ethyl group, a trifluoromethyl group, or a trichloromethyl group; and Ar represents a residue of an aromatic tetracarboxylic acid.
Although the above-described polyimide oriented film has excellent transparency, it is still colored yellow and has not been proved to be entirely satisfactory for use as a liquid crystalline oriented film.